Power steering apparatus for nose wheels



May 2, 1950 s, MacDUFF 2,506,093

POWER STEERING APPARATUS FOR NOSE WHEELS Filed June 5, 1947 2 Sheets-Sheet 1 IN VEN TOR.

Patented May 1 950 UNITED STATES PATENT OFFICE POWER STEERING APPARATUS FOR NOSE WHEELS Stanley I. MacDufl', South Bend, Ind., assignor to Bendix Aviation Corporation, South Bend, Ind., a corporation of Delaware Application J nine 5, 1947, Serial No. 752,737

2 Claims. (Cl. ISO-79.2)

This invention relates generally to steering apparatus and more particularly to a steering mechanism for the nose wheel of an aircraft.

One of the important objects of the invention resides in the provision of a power steering apparatus for the nose wheel of an aircraft in which the power for steering is obtained from an open hydraulic system and the control of this power is through the medium of a closed hydraulic circuit.

An important object of the invention lies in the provision of a hydraulic steering apparatus connected to a steered member in a manner to transmit motion thereto whereupon the cause producing said motion is nullified by the movement of said member.

The above and other objects and features of the invention will be apparent from the following description of the apparatus taken in connection with the accompanying drawings which form a part of this specification, and in which:

Figure l exemplifies diagrammatically the apparatus of the invention; and

Figure 2 shows parts of the apparatus mounted on a shock strut for guiding the nose wheel associated therewith.

The apparatus of Figure 1 comprises essentially a closed hydraulic system and an open hydraulic system. The closed system includes a transmitter unit I0, receiver unit I2, temperature compensating mechanism I4, and conduits I8, I8, 28, and 22 interconnecting the aforementioned units and the mechanism. The open system includes a fluid motor 24, valve 26, accumulator 28 for storing fluid under pressure from a pump 30, a fluid reservoir 32, and a regulator valve 34 for bypassing fluid to the reservoir when the fluid under pressure in the accumulator reaches a predetermined value. One end of the motor is in communication with the accumulator through conduits 36 and 3t; and the other end of the motor is in communication with the reservoir through conduits 40 and 42. The valve 26 is interposed between conduits 36 and 38, and conduits 40 and 42 respectively to control the now of fluid to the ends of the motor. The regulator valve, which is of a type shown in my ap lication for patent Serial Number 451,593, filed July 20, 1942, now Patent No. 2,420,890, dated May 20, 1947, is interposed between the conduit 28, and conduits 44 and 48, the latter conduitsrespectively, connecting the regulator valve to the outlet of pump 30 and to the conduit 42. Conduit 4i connectsthe reservoir to the pump. Conduits II and I2 interconnect the open and closed systems for supplying fluid to the latter as desired.

2 Valves 54 and 58 are located in conduits 50 and 52 respectively for manual control.

' The fluid motor 24 includes a cylinder 50 having a piston 60 therein, dividing the cylinder into oppositely disposed chambers 62 and 64, connected to the conduits 36 and 40 respectively. A piston rod 6| has one end fixed to the piston 60 and its other end protruding beyond the end of the cylinder.

To control the flow in the open hydraulic system between the source and the motor 24 the valve 26 is provided. The valve comprises a body 65, with a bore 86 therein. An inlet port 68, cylinder ports It and I2, and return port 14 are formed in the body and open into the bore at axially spaced positions therein. The bore 60 is recessed at 1B and I8 to form valve seats 00 and 82 respectively on which co-axially arranged hollow valve members 84 and 86 normally seat to cut off flow to the cylinder 58. A passage 88 connects the recesses I6 and 18 which are axially spaced apart in the bore. A spring 90 is'interposed between the inner or adjacent ends of the valve members so as to urge them in opposite directions against the valve seats. For unseating the valve members a rod 92 is provided which extends longitudinally through the bore and is equipped with bushings 94 and 96 constituted to engage one end of one or the other of the hollow valve members 84 and 06 respectively depending upon the direction of movement of the rod. The rod is normally held in a position by spring 98 so that the bushings 94 and 96 are out of engagement with the ends of the hollow valve members to permit communication between the chambers 62 and 64 and the return port 14, via the interior of the hollow valve members.

The transmitter unit I2 comprises a cylinder I00 having a piston IOI therein, dividing the cylinder into two chambers, one at each end thereof. The piston is provided with a rack I02, integral therewith. A shaft I03 is rotatably carried by the cylinder in transverse relationship thereto and provided with gears I04 and I05 fixed to opposite ends of the shaft. A steering device or wheel I06 is spllned or otherwise securely fastened to one end of a shaft I01 having a pinion gear I08 suitably secured thereto at the other end for driving engagement with gear I05 to thereby impart reciprocal motion to piston IOI through rotative motion of the wheel. A conduit IIO connects the ends of the cylinder I00. A bleed or centering valve I I2 is located in the conduit I." for manual operation to thereby control 3 communication between the ends of cylinder I" to permit centering the piston IUI therein.

The receiver unit includes a cylinder II4 having a piston II6 reciprocally positioned therein and dividing the cylinder into two opposed chambers. The cylinder is formed with openings III and I26 in its ends for connecting the receiver with the transmitter through conduits I6, I8, 26 and 22. A piston rod I22 is integrally related to the piston and extends through the ends or the cylinder to thereby provide equal effective areas on the opposite sides of the piston. One end of the piston rod I22 is formed at I24 to be fastened to a lever I26. The lever is integral with a collar I26 at one end and is rotatably carried by a shock strut I30. The lever I26 is connected at its other end to the piston rod 6i or the fluid motor. The cylinder Ht oi'the receiver is movable relative to the piston H8. A lever Hi2 operatively ties the cylinder Ii! and the rod t2 together so that movement of the cylinder operates the valve members 84 and 8G. The lever use is fulcrumed on a pin ltd carried by e linlr tilt supported by the valve body 65.

To compensate for pressure changes in the closed hydraulic system due to variation in temperature of the fluid in the system the compensating mechanism id is provided. The temperature compensating mechanism per se is claimed in my application Serial Number 704,261, filed Oct. 18, 1946. The mechanism includes a valve member Mil seated in a passage Mi which communicates conduits it and it with a reservoir $42, the interior of which is divided, by a hexible diaphragm M3, into an upper chamlmr 6418, into which air is pumped under pressure, and a lower chamber I 45 in communication with passage I4i, whereby any change in volume of fluid in the system is accounted for in the reservoir 842. The valve member Mil has a stem M6 inteam! with a head it'll, which is biased onto a valve seat M8 located in the passage Hit, by a spring hit, to thereby normally cut oil com munication between the chamber its, and conduits i and I8. The valve stem Mt has one end terminating in a passage E56 which connects conduit Zll to conduit 22, to thereby subject said one end of the valve stem to the fluid under pressure existing in the latter conduits. A seal I52 encircles the valve stem to prevent leakage between the passage I50 and conduits I6 and i8, axially along the valve stem. The efiective annular area I54 of the valve head formed between the valve seat I48 and the valve stem, and on which the pressure in lines I6 and I6 acts when the valve member is seated, is made equal to the efiective area we of the valve stem I46 on which the pressure in lines 20 and 22 acts. As shown the spring H49 is selected to exert a force on the valve member equal to substantially one-half the total operating force required for the system. Actually, however, the total force holding the valve member Mil on its seat is the summation of the force of spring I49 plus the pressure of the fluid in chamber I45 acting on the enlarged head I41 of the valve member. A check valve N50 is located in a passage I62 which connects the chamber I45 to conduits I6 and I8, to thereby permit the flow of fluid from the chamber to these conduits but preclude flow in the opposite direction. The conduit 50 is connected into the passage I62 to supp y fluid to the closed system when desired. A check valve I64 is interposed between the conduit 60 and the passage I62 to permit flow into asoaoos passage I42 but prevent flow in the opposite direction. A spring I66; is interposed between the check valves I66 and I44 to urge them against their seats. The manually controlled valves 64 and 56 are arranged to normally disconnect the closed hydraulic system from the source.

The shock strut I36 carried by an airplane, not shown, comprises a pair of telescoping tubes I16 and H2. The tube I'll is equipped with a flange II4 for supporting the rotatable collar H26. A bracket I16 is carried by the tube I'll for supporting the motor 24 and receiver I2. The tube 572 is provided with a collar I'It securely iastened thereto against rotation. A scissors connection I86 connects the rotatable collar I24 to the collar Iii to allow for axial displacement of the tubes relatlveto each other and to impart rotative movement to tube I12 about its axis to thereby guide a nose wheel or steered member M2, carried by an axle I integral with tube I12.

Operation oi the apparatus is'as follows:

With the parts of the apparatus in the position shown in Figure i. assume steering wheel M6 is rotated in a direction to move piston IOI to the left. This puts the fluid in conduits I6 and i3, and in the upper end of the receiver cylinder it under pressure. since the resistance offered by the piston, which is drivably connected to the wheel through the aforementioned linkage, is greater than the resistance oflered by the cylinder which is operatively connected to the valve rod 82, the latter is moved in response to movement or the cylinder upwardly. That is, upward movement of the cylinder pivots the lever i232 about pin I38 which moves the rod 52 downwardly. Movement of the rod 82 downwardly carries busmng 94 with it into engage:

ment with one end of the hollow valve member 84. Initial engagement between the bushing94 and the valve member 64 cuts ofi communication between chamber 64 of the motor and return port id, through the hollow valve member, and continued movement of the rod downwardly unseats valve member 86 from seat Bil to thereby counicate inlet port 58 with the chamber 66, through passage 88 oi the valve body. At this e chamber 62 is in communication with return port I4, via conduit 36, and the interior of hollow valve member 36. This subjects piston 69 to a difierential in pressure, with the greater force acting in a direction to move the piston downwardly, thereby rotating the collar I28 which imparts rotation to the tube I12 through the scissors connection it, whereby wheel I82 is guided. Rotation of lever I26 in a clockwise direction by piston 60 also tends to move receiver piston II6 downwardly within the cylinder. but because of the incompressibility of the fluid medium iii the ends of the cylinders II4 and I66, and, in the conduits 28 and-22, the receiver is moved downwardly as a unit pivoting around pin I34. This returns rod 82 to the position shown in the figure. Spring 98 centers the rod 62 in the cylinder and the valve member 64 is seated by'spring 90. This arrangement provides a follow up system for cutting oil the flow to the motor. To turn the nose wheel I62 back to its original position the 1. A hydraulically actuated power steering apparatus for an aircraft having a steering device and a steered member, said apparatus comprising a fluid motor drivably connected to said steered member, a source of fluid under pressure having a connection to said motor, a valve in the connection, said valve shiftable from a. normally closed position in which the motor is cut off from said source to an open position v where communication is established between the source and the motor, a closed hydraulic system including said steering device and a receiver unit responsive to movement of said steering device, a mechanical connection operatively connecting the receiver unit to the valve to move the same to open position to thereby connect the motor to said source, whereupon the motor moves said steered member, means in the closed hydraulic system to compensate for pressure changes therein due to temperature variation of the fluid, and means connecting the motor to the receiver for returning said valve to closed position as the steered member is moved to thereby provide a follow up control.

2. A hydraulic actuated power steering apparatus for an aircraft having a steering device and a steered member, said apparatus comprising a fluid motor drivably connected to said steered member, a source of fluid under pressure having a connection to said motor, a valve in the connection, said valve shittable from a 6 normally closed position in which the motor is cut oil from said source to an open position where communication-is established between the source and the motor, a closed hydraulic system including said steering device and a receiver unit responsive to movement of said steering device, a pair of conduits connecting the steering device to said receiver unit, means providing a connection between the receiver unit and valve to move the latter to open position to thereby connect the motor to said source, whereupon the motor moves said steered member, means in the closed hydraulic system for compensating for pressure changes therein due to variations in temperature in fluid and including a device in communication with one of said conduits and operative to effect release of the fluid from said one conduit upon a temperature rise and force fluid thereinto upon a temperature drop, and means connecting the motor to the receiver for returning said valve to closed position upon movement of the steered member.

STANLEY I. MACDUFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'IENTS Number Name Date 2,252,660 Kulikofl Aug. 12, 1941 2,401,364 Mercier June 4, 1946 2,418,325 Wassall et al Apr. 1, 1947 2,424,233 Greenough July 22, 1947 FOREIGN PATENTS Number Country Date 527,013 Great Britain Oct. 1, 1940 

